Analysis of temperature effect in dielectric response of electrostrictive polymers for pseudo-pyroelectric operations

Thanks to their flexibility and easy processability, electroactive polymers have gained a lot of attention over the last decades. More specifically, dielectric electrostrictive polymers have been demonstrated to provide interesting ways for mechanical actuation and energy harvesting or for electrocaloric applications. This Letter aims at presenting an additional application potential of such materials, showing their ability in terms of converting thermal energy into electrical energy. More particularly, it is shown that such materials, once polarized through the application of a bias electric field, allow a polarization variation with the temperature, yielding the so-called pseudo-pyroelectric effect. Theoretical analysis, supported by experiments, therefore demonstrates that such a material can exhibit pseudo-pyroelectric activity that can be tuned with the applied electric field.     

Real time inverse filter focusing through iterative time reversal

In order to achieve an optimal focusing through heterogeneous media we need to build the inverse filter of the propagation operator. Time reversal is an easy and robust way to achieve such an inverse filter in nondissipative media. However, as soon as losses appear in the medium, time reversal is not equivalent to the inverse filter anymore. Consequently, it does not produce the optimal focusing and beam degradations may appear. In such cases, we showed in previous works that the optimal focusing can be recovered by using the so-called spatiotemporal inverse filter technique. This process requires the presence of a complete set of receivers inside the medium. It allows one to reach the optimal focusing even in extreme situations such as ultrasonic focusing through human skull or audible sound focusing in strongly reverberant rooms. But, this technique is time consuming and implied fastidious numerical calculations. In this paper we propose a new way to process this inverse filter focusing technique in real time and without any calculation. The new process is based on iterative time reversal process. Contrary to the classical inverse filter technique, this iteration does not require any computation and achieves the inverse filter in an experimental way using wave propagation instead of computational power. The convergence from time reversal to inverse filter during the iterative process is theoretically explained. Finally, the feasibility of this iterative technique is experimentally demonstrated for ultrasound applications.     

Combined first-principles computational and experimental multinuclear solid-state NMR investigation of amino acids

13C, 14N, 15N, 17O, and 35Cl NMR parameters, including chemical shift tensors and quadrupolar tensors for 14N, 17O, and 35Cl, are calculated for the crystalline forms of various amino acids under periodic boundary conditions and complemented by experiment where necessary. The 13C shift tensors and 14N electric field gradient (EFG) tensors are in excellent agreement with experiment. Similarly, static 17O NMR spectra could be precisely simulated using the calculation of the full chemical shift (CS) tensors and their relative orientation with the EFG tensors. This study allows correlations to be found between hydrogen bonding in the crystal structures and the 17O NMR shielding parameters and the 35Cl quadrupolar parameters, respectively. Calculations using the two experimental structures for L-alanine have shown that, while the calculated isotropic chemical shift values of 13C and 15N are relatively insensitive to small differences in the experimental structure, the 17O shift is markedly affected.     

Eco-friendly process toward collector- and binder-free,high-energy density electrodes for lithium-ion batteries

Journal of Solid State Electrochemistry - The preparation of collector- and binder-free, high-energy density cathodes made from carbon-coated LiFePO4 (C-LFP) and single-walled carbon nanotubes...     

A Maltol-Containing Ruthenium Polypyridyl Complex as a Potential Anticancer Agent

Cancer is one of the main causes of death worldwide. Chemotherapy, despite its severe side effects, is to date one of the leading strategies against cancer. Metal-based drugs present several potential advantages when compared to organic compounds and they have gained trust from the scientific community after the approval on the market of the drug cisplatin. Recently, we reported the ruthenium complex ([Ru(DIP)₂(sq)](PF₆) (where DIP is 4,7-diphenyl-1,10-phenantroline and sq is semiquinonate) with a remarkable potential as chemotherapeutic agent against cancer, both in vitro and in vivo. In this work, we analyse a structurally similar compound, namely [Ru(DIP)₂(mal)](PF₆), carrying the flavour-enhancing agent approved by the FDA, maltol (mal). To possess an FDA approved ligand is crucial for a complex, whose mechanism of action might include ligand exchange. Herein, we describe the synthesis and characterisation of [Ru(DIP)₂(mal)](PF₆), its stability in solutions and under conditions that resemble the physiological ones, and its in-depth biological investigation. Cytotoxicity tests on different cell lines in 2D model and on HeLa MultiCellular Tumour Spheroids (MCTS) demonstrated that our compound has higher activity than cisplatin, inspiring further tests. [Ru(DIP)₂(mal)](PF₆) was efficiently internalised by HeLa cells through a passive transport mechanism and severely affected the mitochondrial metabolism.     

Electrochemical behaviour and voltammetric sensitivity at arrays of nanoscale interfaces between immiscible liquids

Arrays of nanoscale interfaces between immiscible electrolyte solutions were formed using silicon nitride nanopore array membranes. Nanopores in the range from 75 nm radius down to 17 nm radius were used to form the nano-interfaces. It was found that the liquid organic phase electrolyte solution filled the pores so that inlaid nano-interfaces were formed with the aqueous phase. Cyclic voltammetry at these nano-interface arrays demonstrated steady-state behaviour at the larger interfaces but the voltammetric wave-shape became progressively worse as the interface size decreased. It was found that the ion transfer currents were ca. 50% of those expected based on theoretical calculations, which is attributed to overlap of diffusion zones at adjacent nano-interfaces. Here, the separation between adjacent nano-interfaces was 20-times the interface radius. The analytical sensitivity for ion transfer from the aqueous to the 1,6-dichlorohexane organic phase was estimated from calibration plots of current density versus concentration of aqueous tetraethylammonium cation. The sensitivity was in the range of 65 μA cm(-2) μM(-1) (at 75 nm radius interfaces) to 265 μA cm(-2) μM(-1) (at 17 nm radius interfaces). The sensitivity depended directly on the inverse of the nano-interface radius, implying that smaller interfaces will provide better sensitivity, due to the enhanced flux of analyte arising from convergent diffusion to smaller electrochemical interfaces.     

Theoretical and experimental studies of CH3X-Y2 rotational line shapes for atmospheric spectra modelling: application to room-temperature CH3Cl-O2

The case of symmetric tops CH(3)X (X = Br, Cl, F, …) perturbed by non-polar diatoms Y(2) (Y = N(2), O(2), …) is analysed from the viewpoint of theoretical collisional broadening of their rotational lines observed in atmospheric spectra. A semi-classical approach involving an exponential representation of the scattering operator and exact trajectories governed by the isotropic potential is presented. For the first time the active molecule is strictly treated as a symmetric top and the atom-atom interactions are included in the intermolecular potential model. It is shown for the CH(3)Cl-O(2) system that these interactions contribute significantly to the line width for all values of the rotational quantum numbers J and K. Additional testing of modifications required in the semi-classical formalism for a correct application of the cumulant expansion is performed and it is shown that the use of the cumulant average on the rotational states of the perturbing molecule leads to entirely negligible effects for the not very strongly interacting CH(3)Cl-O(2) system. In order to check the theoretical predictions and to extend the scarce experimental data available in the literature to higher values of the rotational quantum numbers, new measurements of room-temperature O(2)-broadened CH(3)Cl rotational lines are carried out by a photomixing continuous-wave terahertz spectrometer. The experimental line widths extracted with a Voigt profile model demonstrate an excellent agreement with theoretical results up to very high J-values (J = 31, 37, 40, 45, 50).     

Hydrolysis and grafting of dimethylalkoxysilanes onto stainless steel

The grafting of trialkoxysilane molecules should also give rise to the formation of a siloxane network at the substrate's surface when trialkoxysilanes are used. Other candidates that might be able to act as adhesion promoters at metallic surfaces are dimethylalkoxysilanes. The advantage of dimethylalkoxysilanes is that only one silanol group is produced during the hydrolysis step, leading to the formation of a grafted monolayer onto the steel. Moreover, the chemical grafting of stainless steel, which exhibits a low surface reactivity, is of great interest for industrial applications such as adhesive bonding or coatings. The objective of this work was to chemically graft dimethylalkoxysilanes onto AISI 316L stainless steel and to analyze the grafted layer by X‐ray photoelectron spectroscopy (XPS). Investigation of the hydrolysis of these molecules in aqueous solutions was also performed by proton nuclear magnetic resonance spectroscopy (¹H NMR). The grafting of 3‐(ethoxydimethylsilyl)propylamine (APDES) and 3‐glycidoxypropyldimethylethoxysilane (GPDES) was achieved onto stainless steel after a controlled hydrolysis reaction. A pH inferior or equal to 5 was necessary to obtain a sufficient hydrolysis of silanes. XPS results have evidenced the grafting of the silanes onto stainless steel. The signal of the Si 2p peak clearly showed the formation of a covalent bond between APDES and the stainless steel surface through the O atoms giving rise to a uniform layer of adsorbed molecules. Moreover, this grafted layer is strongly stable as no removal of the alkoxysilane was observed after immersion in hot water which is very critical for these molecules. Copyright © 2015 John Wiley & Sons, Ltd.